The other aspect that John's trivia totally fails to address is that the
health benefit of cycling or walking will most likely lead to lower energy
usage.

When I started cycling to work in 2005, I was very overweight. I combined
cycling with being sensible about my diet (thus eating less straight off,
not more). Within 3 months I had lost 19 Kg of weight, so clearly I was
using significantly less energy to get myself around throughout the day. On
holiday in Paris late that summer I climbed up the first two stages of the
Eiffel tower with hardly any effort at all - just sailed up, whereas before,
it would have reduced me to a gasping heap.

Sadly, due to my weakness for food that's bad for me I have put much of it
back on since then, but that clearly wasn't to do with cycling - it was to
do with gluttony :-(

> The trivia you mention below is a fallacy. From David McKay's "Sustainable
> Energy - Without All the Hot Air"
> (Book is available on-line)
>
> Here is an excerpt from his "Mythconceptions" section on p. 79:
>
>
> "I heard that the energy footprint of food is so big that â€œitâ€™s better to
> drive"
>
> Whether this is true depends on your diet. Itâ€™s certainly possible to find
> food whose fossil-fuel energy footprint is bigger than the energy delivered
> to the human. A bag of crisps, for example, has an embodied energy of
> 1.4 kWh of fossil fuel per kWh of chemical energy eaten. The embodied
> energy of meat is higher. According to a study from the University of
> Exeter, the typical diet has an embodied energy of roughly 6 kWh per kWh
> eaten. To figure out whether driving a car or walking uses less energy, we
> need to know the transport efficiency of each mode. For the typical car
> of Chapter 3, the energy cost was 80 kWh per 100 km. Walking uses a net
> energy of 3.6 kWh per 100 km â€“ 22 times less. So if you live entirely on
> food whose footprint is greater than 22 kWh per kWh then, yes, the energy
> cost of getting you from A to B in a fossil-fuel-powered vehicle is less
> than
> if you go under your own steam. But if you have a typical diet (6 kWh per
> kWh) then â€œitâ€™s better to drive than to walkâ€